In recent years, liquid crystal display devices that are characterized by their thinness and light weight are widely used as display devices for the display of personal computers and the display section of mobile information terminals. However, conventional Twisted Nematic mode (TN mode) and Super Twisted Nematic mode (STN mode) liquid crystal display devices disadvantageously have narrow viewing angles. To solve this problem, various technical developments have been made.
A known example of liquid crystal display devices which have improved viewing angle characteristics is a divisional alignment type liquid crystal display device which includes a vertical alignment type liquid crystal layer. A liquid crystal display device of this type is called a VA (Vertical Alignment) mode liquid crystal display device. As one example of the VA mode, Patent Document 1 discloses a MVA (Multi-domain Vertical Alignment) mode. In the MVA mode, each of a pair of substrates which oppose each other with the intervention of a liquid crystal layer has an alignment regulating structure for regulating the alignment of liquid crystal molecules. Specifically, the alignment regulating structure may be a protrusion or a slit formed in an electrode. With the alignment regulating structure such as a protrusion and a slit, a plurality of domains among which the azimuth of inclination of liquid crystal molecules is different are formed when a voltage is applied across the liquid crystal layer, so that the viewing angle characteristics are improved.
Patent Document 2 proposes a different type of VA mode, which is called a CPA (Continuous Pinwheel Alignment) mode. In the CPA mode, one of a pair of electrodes that oppose each other with the intervention of a liquid crystal layer has an opening or notch. An oblique electric field which is generated above the opening or notch is utilized to radially incline liquid crystal molecules, whereby a wide viewing angle is realized.
Patent Document 3 discloses a technique of stabilizing a radial inclination alignment of liquid crystal molecules in the CPA mode. According to this technique, a radial inclination alignment formed by an alignment regulating structure provided in one of the substrates (an opening or notch formed in an electrode, which contributes to generation of an oblique electric field) is stabilized by another alignment regulating structure (e.g., protrusion) provided in the other substrate.
On the other hand, providing a polymer structure as an alignment sustaining layer for regulating the pretilt angle and the pretilt direction of liquid crystal molecules is proposed in, for example, Patent Documents 4, 5, 6, and 7. This is called a PSA (Polymer-Sustained Alignment) technology. The polymer structure is formed by photopolymerizing or thermally polymerizing a polymerizable composition contained beforehand in the liquid crystal layer. By providing such a polymer structure in a VA mode liquid crystal display device, the alignment stability and the response characteristics can be improved.